We used a 5" handle on our smallest drawer , ~8" handles on most other drawers and doors, 12" ones on the trash can cab, DW, and wide cab over the fridge. Looks good to us! :-)

Mine are all 4":

I have one pull on drawers These are 24" drawers (the drawers on the right, over & below the warming drawer, are 30"):

Our pull came in three widths. We bought one of each and then used Museum Wax to temporarily hold the pulls in place. That helped a lot for us.

In terms of the standard, 3inch is the American standard and 96mm is the European standard. Of course, there are many other sizes...